Anisotropic scattering sheet and its use

ABSTRACT

An anisotropic scattering sheet is adapted to scatter an incident light in a light-advancing direction and has a light-scattering characteristic F(θ) that satisfies the following expression representing a relation between a light-scattering angle θ and a scattered light intensity F over a range of θ=4 to 30°: Fy(θ)/Fx(θ)&gt;2, wherein Fx(θ) represents the light-scattering characteristic in a direction of a X-axis and Fy(θ) represents a light-scattering characteristic in a Y-axial direction which is perpendicular to the X-axial direction.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP01/09134 which has an Internationalfiling date of Oct. 18, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to an anisotropic scattering or diffusingsheet which is capable of illuminating a display unit of a displayapparatus (in particular, a transmittable (transmission type) liquidcrystal display apparatus) uniformly and inhibiting a change of theluminance even when a visual angle on or to a display surface changes, aplane light source unit using the sheet (a backlight unit or device),and a display apparatus using the unit (particularly, a transmittabledisplay apparatus such as a transmittable liquid crystal displayapparatus). Specifically, the present invention relates to ananisotropic scattering or diffusing sheet which is capable of inhibitinga change of the luminance even when a visual angle somewhat changes inthe across direction (horizontal direction) on a display surface of atransmittable liquid crystal display apparatus and being employedwithout effecting eyestrain, a transmittable liquid crystal displayapparatus using the sheet, and a plane light source device thereof.

BACKGROUND ART

In a backlight type display apparatus (a liquid crystal displayapparatus) illuminating a display panel (e.g., a liquid crystal displaymodule) from its backside, a flat or plane light source unit (or abacklight unit) is disposed on the backside of the display panel. Theplane light source unit comprises, for example, a tubular light sourcesuch as fluorescent tube (cold cathode tube) disposed adjacent to alateral side of a light guide, the light guide for guiding a light fromthe tubular light source to a display panel, and a reflector disposedopposite to the display panel side of the light guide. In such a planelight source unit, since a light from a fluorescent tube is reflected bythe reflector and guided by a light guide, a diffusing or scatteringfilm is usually disposed between the tubular light source and thedisplay panel for uniformly illuminating the display panel from behind.As the diffusing film, a transparent and highly heat-resistantpolycarbonate film or a polyester film each comprising dispersed resinmicrofine particles (resin beads) or light-transmissive inorganicmicrofine particles is employed. However, even when such a diffusingfilm is used, it is inevitable due to its isotropy of light diffusingthat the luminance in a certain direction (the axis-direction of thefluorescent tube) is unduly lowered. As a result, it is unable toilluminate the display panel uniformly with the high luminance.

Therefore, in Japanese Patent Application Laid-Open No. 231315/1999(JP-11-231315A), 84357/1999 (JP-11-84357A) and 84376/1999(JP-11-84376A), an optical element such as a prismatic lens isinterposed between the diffusing film (diffuser) and the liquid crystallayer to thereby refract the diffused light so that the light will beincident perpendicularly on the liquid crystal display surface, thusupholding the luminance.

More specifically, Japanese Patent Application Laid-Open No. 231315/1999(JP-11-231315A) discloses a plane light source unit comprising a linearlight source such as a fluorescent tube, a light guide on which a lightfrom the linear light source is incident from the lateral side, adiffusion reflector disposed adjacently to the bottom surface of thelight guide, a reflecting mean composed of concavity/convex formed onthe bottom surface of the light guide (e.g., a prismatic system).

Japanese Patent Application Laid-Open No. 84357/1999 (JP-11-84357A)discloses a liquid crystal display apparatus comprising a backlightunit, a liquid crystal display panel disposed on the unit, a first lenssheet interposed between the backlight unit and the liquid crystaldisplay panel, and a change or switching means for changing the firstlens sheet to a second lens sheet. The literature also describes atechnology that a light from a fluorescent tube is guided from thelateral side of the light guide to an emerging surface, a light from theemerging surface is focused by a lens sheet in which a plurality oftriangle-shaped sectional prisms are formed in parallel with each other,thereby a display panel is illuminated.

Such a device or unit enables to focus the diffused light with use of aprism for illuminating the display panel with the high luminance.However, an uneven emission (luminance) distribution in the directionperpendicular relative to the longitudinal direction of the fluorescenttube is inevitable, causing a streak pattern to appear, although theemission distribution in the longitudinal direction of the fluorescenttube is uniform. Therefore, it is difficult to illuminate the displaypanel uniformly.

Japanese Patent Application Laid-Open No. 84376/1999 (JP-11-84376A)discloses, as a unit for illuminating a transmittable liquid crystaldisplay panel with uniform luminance, a backlight unit comprising alight guide for guiding a projected light to the display panel, afluorescent lamp disposed in proximity to one side of the light guide, areflector for reflecting a light from the fluorescent lamp toward afront direction (a direction of a display panel), a diffusion plate(diffuser) for diffusing a emerge light from an emerging surface of thelight guide to be uniformed, which is disposed on the front side of thelight guide, and a prism sheet for gathering a light from the diffusionplate. The literature describes an example of a unit comprising a pairof prism sheets disposed oppositely with aligning the extended directionof the prisms toward a crossing direction each other, and diffusionplates disposed on both sides of the prism sheets.

Since a plurality of prism sheets and a plurality of diffusers arerequired for such a backlight unit, its structure is complicated and itsluminance is lowered. Moreover, even when the above backlight unit isemployed, its luminance distribution is not still uniform. Thus,although an emission distribution (luminance distribution) in thelongitudinal direction (X-axis direction) of the fluorescent tube (coldcathode tube) is relatively uniform, the emission distribution(luminance distribution) in the Y-axis direction perpendicular to theX-axis direction of the fluorescent tube has a streak-likedirectionality (linear dark areas) and is not still uniform.

For example, as a plane or flat display apparatus of which the imagedisplay area has a flat surface (a flat type display apparatus), anapparatus as illustrated in FIG. 8 is known. The apparatus comprises aflat display unit (e.g., a transmittable liquid crystal display unit) 45and a flat light source unit adapted to illuminate the display unit fromits back side. The plane or flat light source unit comprises at leastone fluorescent discharge tube (cold cathode tube) 41, and a reflector42 is disposed on the back side of the fluorescent discharged tube 41for reflecting a light, a diffuser 43 is interposed between thefluorescent discharged tube 41 and a display unit 45 for diffusing thelight to uniformly illuminate the display unit 45, and a prism sheet 44is laminated on the unit side of the diffuser 43. The flat display unit45, in the case of a liquid crystal display unit, comprises a firstpolarizing film 46 a, a first glass substrate 47 a, a first electrode 48a on the glass substrate, a first alignment layer 49 a laminated on theelectrode, a liquid crystal layer 50, a second alignment layer 49 b, asecond electrode 48 b, a color filter 51, a second glass substrate 47 b,and a second polarizing film 46 b as successively built up (laminated)in that order. In such a display apparatus, the display unit can bedirectly illuminated from the back side by the built-in fluorescent tube(cold cathode tube) 41.

Moreover, an apparatus comprises a backlight unit having such a lightguide as illustrated in FIG. 9 as the backlight system of the flatdisplay apparatus of FIG. 8 has been known. This backlight unit has afluorescent tube (cold cathode tube) 51 and a reflector member 55disposed in parallel with the fluorescent tube, with a light guide 54having a diffuser 53 at top and a reflector 52 at bottom being disposedin the direction of light emission from the fluorescent tube.Incidentally, the thickness of the light guide 54 at the fluorescenttube side is larger than that of the other side, so that the light fromthe fluorescent tube 51 can be reflected in a forward direction. Thelight emerged from the emerging surface of the light guide is diffusedby the diffuser 53 and incident on the flat display apparatus (notshown) constructed (laminated) on the diffuser.

When such a backlight unit is used, a display panel can be illuminatedby focusing a diffused light with use of a prism sheet, and in contrastto the backlight unit or component of FIG. 8, the emission distributionmay appear uniform over the surface but a detailed observation of theemission distribution reveals that the distribution is still not asuniform as desired. Thus, as shown in FIGS. 10 and 11, the emissiondistribution (luminance distribution) in the longitudinal (axial)direction (X-direction) of the fluorescent tube (cold cathode tube) 51is relatively uniform as it is the case in the apparatus or device ofFIG. 8 but the emission from the fluorescent tube (cold cathode tube) inthe Y-direction which is perpendicular to the X-direction is repeatedlyreflected by the reflector 52 and advances in the Z-direction (such adirection as the liquid crystal display unit is disposed) which isperpendicular to the XY plane so that the emission distribution(luminance distribution) in the Y-direction is distorted (in a zigzagpattern), thus failing to uniform the luminance distribution.

Thus, in the usual backlight type display apparatus, the emissiondistribution (luminance distribution) in the direction perpendicular tothe longitudinal direction (X-direction) of the fluorescent tube is notuniform and a streak-like directionality (linear dark areas) is producedin the emission distribution. In order to improve in uniformity of theluminance, a diffusing film having an excellent light-diffusing propertymay be used. However, usually, a diffusing film is scattered an incidentlight isotropically, and as a scattering angle becomes larger, ascattering intensity decreases greater. Referring to the degree ofdecrease in the scattering intensity when the scattering angle becomeslarger, in the case of a commonly used diffusing film, in about 9° ofthe half width, the decay (extinction) of the intensity is, for example,F(0°)/F(18°)=about 12 and F(0°)/F(23°)=about 60, wherein θ representsthe scattering angle, and F represents the scattered light intensity (orthe intensity of scattered light), and the decay of the scatteringintensity is extreme depending on the angle. Therefore, the intensity oflight scattered at 30° or more of the scattering angle is very small.

From such a viewpoint, use of a prism sheet improves the luminance at ascattering angle from the front to 20°. That is, regarding the directionthat a prism sheet focuses a light, use of one piece of the prism sheetcan make widely the scattering angle to about 18°. However, if thescattering angle is more than 18°, the scattering intensity (luminance)decreases rapidly. In case of the method in which two pieces of theprism sheet is disposed in the direction perpendicular to each other,the luminance of the display apparatus can be uniform isotropicallywithout depending on the angle. However, the angle is not more thanabout 20° in length and breadth. When the scattering angle is more than20°, the luminance is deteriorated rapidly in comparison with theluminance in the case of using no prism sheets.

Such display apparatus restricts an angle of vision (visual angle orviewing angle) for a user of the display apparatus, and therefore, theuser can not recognize the display of the display surface visually in awide angle. Thus the display apparatus is inconvenient and effects asense of fatigue. Therefore, a diffusing sheet, which can scatter alight over a wide range of the angle has investigated. However, in sucha diffusing sheet, the luminance is extremely deteriorated. Accordingly,in order to improve in the luminance, a light source having strongemission ability should be used.

Japanese Patent Application Laid-Open No. 314522/1992 (JP-4-314522A)describes an anisotropic light-scattering material comprising atransparent matrix and a transparent substance which is morphologicallyanisotropic and differing in the index of refraction (the refractionindex) from the transparent matrix as uniformly dispersed in the matrixin a positional relation shifted in an orderly and mutually parallelmanner. Moreover, the literature discloses the preferred range of theaspect ratio of morphologically anisotropic substance is 15 to 30 andthe length of minor axis is 1 to 2 μm. Specifically, the anisotropiclight-scattering material is manufactured by a method which compriseskneading a low-melting low-density polyethylene for the transparentmatrix resin with a high-melting polystyrene or a styrene-acrylonitrilecopolymer for the transparent substance, extruding the resultingcomposition, and cooling the molten resin extruded in the form of asheet under stretching with a large draft in the direction of extrusion.The anisotropic light-scattering material has been used as a lenticularlens for the projection television screen.

Japanese Patent Application Laid-Open No. 114013/1995 (JP-7-114013A)discloses a liquid crystal display apparatus in which a film or a sheetcapable of scattering and transmitting an incident light is disposed ona display screen in order to improve in viewing angle properties. Theliterature discloses a film or a sheet in which a dispersed phaseparticle composed of a transparent resin and having a ratio oflongitudinal axis to minor axis of not less than 10 and an averageparticle size of 0.5 to 70 μm is dispersed in a transparent resinmatrix.

However, in a display apparatus with the use of a tubular light sourcehaving anisotropy in an emission distribution (luminance distribution),it is difficult to illuminate a display panel with uniform luminanceeven if using these films or sheets.

It is, therefore, an object of the present invention to provide ananisotropic scattering or diffusing sheet which is capable of inhibitingthe decrease or deterioration of the luminance depending on an anglerelative to a display surface of a transmittable display apparatus (inparticular, a transmittable liquid crystal display apparatus) andcapable of decreasing an angle dependence on the luminance, a plane orflat light source unit utilizing the sheet, and a transmittable displayapparatus utilizing the plane or flat light source unit (a transmittableliquid crystal display apparatus).

It is another object of the present invention to provide an anisotropicscattering or diffusing sheet which is capable of expanding or enlarginga visual angle relative to a display surface and recognizing the displaysurface visually in the high luminance, a plane or flat light sourceunit utilizing the sheet, and a transmittable display apparatusutilizing the sheet (a transmittable liquid crystal display apparatus).

It is still another object of the present invention to provide ananisotropic scattering or diffusing sheet which is capable ofsuppressing the deterioration of the luminance in a certain directioneven when an angle relative to a display surface exceeds 20°, a plane orflat light source unit utilizing the sheet, and a transmittable displayapparatus utilizing the plane or flat light source unit.

It is further object of the present invention to provide an anisotropicscattering or diffusing sheet which is capable of inhibiting thedeterioration of the luminance in spite of using a tubular light sourcewhich has an anisotropic emission distribution (luminance distribution)and is useful for illuminating a display panel uniformly, a plane orflat light source unit utilizing the sheet, and a display apparatuscomprising the unit (in particular, a liquid crystal display apparatus).

It is still further object of the present invention to provide ananisotropic scattering or diffusing sheet which is capable ofsimplifying the structure, moreover illuminating a display paneluniformly and visually recognizing a display data clearly or finely, aplane or flat light source unit utilizing the sheet, and a displayapparatus utilizing the unit (in particular, a liquid crystal displayapparatus).

DISCLOSURE OF INVENTION

The inventors of the present invention did much research to accomplishthe above objects and found that: by disposing an anisotropic scatteringor diffusing sheet between a light guide member and a display panel, atransmission light through a light-scattering sheet can be scatteredanisotropically to illuminate a display panel uniformly; and that use ofa film having anisotropic light-scattering property in combination witha prism sheet can inhibit the deterioration of the luminance dependingon an angle of a display surface of a transmittable liquid crystaldisplay apparatus (e.g., the luminance of one-direction such as ahorizontal direction). The present invention has been developed on thebasis of the above findings.

That is, an anisotropic scattering sheet of the present invention iscapable of scattering an incident light in the direction of advancethereof (or in light-advancing direction) and having a light-scatteringcharacteristic F(θ) satisfying the following expression representing therelation between the light-scattering angle θ and the scattered lightintensity F over a range of θ=4 to 30°:Fy(θ)/Fx(θ)>2 (for example, Fy(θ)/Fx(θ)>5).

wherein Fx(θ) represents the light-scattering characteristic in thedirection of the X-axis and Fy(θ) represents the light-scatteringcharacteristic in the Y-axial direction which is perpendicular to theX-axial direction. Moreover, in the anisotropic scattering sheet, thescattering characteristic Fx(θ) and scattering characteristic Fy(θ) maysatisfy or fulfill the following expression over a range of θ=2 to 30°:Fy(θ)/Fx(θ)>5 (for example, Fy(θ)/Fx(θ)>10).

Furthermore, the anisotropic scattering sheet may have alight-scattering characteristic Fy(θ) which is decreased gradually withincreasing the light-scattering angle θ larger and the light-scatteringcharacteristic satisfies the following expression representing therelation between the light-scattering angle θ and the scattered lightintensity F over a range of θ=0 to 30°:Fy(0°)/Fy(30°)<200 (for example, Fy(0°)/Fy(30°)<50).

The anisotropic scattering sheet may comprise a continuous phase and aparticulate dispersed phase which are different in the index ofrefraction (or the refractive index) by not less than 0.001 from eachother, the mean aspect ratio of the dispersed phase particles is largerthan 1 and the major axes of the dispersed phase particles are orientedin the X-axis direction of the film. The mean aspect ratio of thedispersed phase particles may be about 5 to 1,000. The mean dimension ofthe minor axes of the dispersed phase particles may be about 0.1 to 10μm. Incidentally, the thickness of the sheet is about 3 to 300 μm andthe total light transmittance of the sheet is not less than 85%.

More specifically, the continuous phase may comprise a crystalline resinsuch as a crystalline polypropylene-series resin. The dispersed phasemay comprise at least one noncrystalline resin selected from anoncrystalline copolyester-series resin and a polystyrenic resin. Theanisotropic scattering sheet may comprise a compatibilizing agent forthe continuous phase and the dispersed phase (for example, an epoxidizeddiene-series block copolymer such as an epoxidizedstyrene-butadiene-styrene block copolymer). The ratio of the continuousphase and dispersed phase is [former/latter]=about 99/1 to 50/50 (weightratio), and the ratio of the dispersed phase and compatibilizing agentis [former/latter]=about 99/1 to 50/50 (weight ratio). The anisotropicscattering sheet may be formed with surface irregularities extending inthe direction of the X-axis of the film or the major axis of thedispersed phase.

The plane or flat light source unit of the present invention comprises atubular light source, a light guide member of which a light from thetubular light source is incident on the lateral side and emerges thelight from an emerge surface, and at least one anisotropic scatteringsheet which is interposed between the light guide member and a displayunit and illuminates the display unit uniformly by the light fromtubular light source. In the plane or flat light source unit, theanisotropic scattering sheet comprises an anisotropic scattering sheethaving the above-mentioned light-scattering characteristic. Such ananisotropic scattering sheet is composed of a continuous phase and adispersed phase which differ in the index of refraction (or therefractive index). The plane or flat light source unit may comprise aplurality of anisotropic scattering sheets. The plurality of anisotropicscattering sheets may be interposed between the light guide member andthe display unit as they have different light-scattering directionalityeach other (e.g., in such a direction as the major axes of the dispersedphases is perpendicular to each other). Two anisotropic scattering sheetmay be interposed between the light guide member and the display unit insuch a direction as the major axes of the dispersed phases isperpendicular to each other.

Moreover, the anisotropic scattering sheet may comprise a continuousphase and a dispersed phase which are different in the index ofrefraction by not less than 0.001 from each other, the mean aspect ratioof the dispersed phase is larger than 1 and the major axis of thedispersed phase is oriented to the axis-direction of the tubular lightsource. For instance, when it is assumed that the axis-direction of thetubular light source is X-axial direction, the anisotropic scatteringsheet may be disposed in Y-axial direction that a main light-scatteringdirection of the anisotropic scattering sheet is perpendicular to theaxis-direction of the tubular light source.

Furthermore, the plane or flat light source unit of the presentinvention may comprise an isotropic scattering sheet interposed betweenthe light guide member and the display unit, a prism sheet, and ananisotropic diffusing sheet having the above-mentioned light-scatteringcharacteristic. In the plane or flat light source unit, usually, thetubular light source is disposed in almost parallel with and adjacent tothe lateral side of the light guide member, a reflective member, whichreflects the light from the tubular light source on the display unitside and is positioned at or on the back of the light guide member, andthe anisotropic scattering sheet is disposed between the light guidemember and the display unit. The anisotropic scattering sheet can bedisposed in the front side of the prism sheet, and when it is assumedthat the axis-direction of the tubular light source is X-axialdirection, the anisotropic scattering sheet may be disposed in such adirection that a main light-scattering direction thereof is addressed ordirected to Y-axial direction.

The display apparatus of the present invention comprises a display unit(e.g., a liquid crystal display unit), and the above-mentioned plane orflat light source for illuminating the display unit. The displayapparatus may be a transmittable display apparatus in which the displayunit comprises a transmittable unit (e.g., a liquid crystal displayunit). In the display apparatus, the anisotropic scattering sheet may bedisposed in various directions (e.g., a direction that a mainlight-scattering direction of the sheet is oriented to the abscissa ofthe display surface in the display unit).

In the display apparatus comprising such a plane or flat light sourceunit, the apparatus is capable of inhibiting a change of the luminanceeven when an angle somewhat changes in the direction to a displaysurface of the display apparatus, and employing without giving a senseof fatigue. For example, a light which passes through an anisotropicscattering sheet is light-scattered in a direction (Y-axial direction)which is perpendicular to the major axis (e.g., the major axis isregarded as X-axial direction). Therefore, in the case where theanisotropic scattering sheet is disposed in a direction which thelongitudinal direction (X-axial direction) of the dispersed phase isoriented or directed to the ordinate on the display surface in thedisplay unit, that is, such a direction as a main light-scatteringdirection (Y-axial direction) is oriented or directed to the lateraldirection (Y-axial direction) of the display surface in the displayunit, the sheet is capable of light-scattering in the abscissa(horizontal direction) at a wide range of the angle. As a result, evenwhen the angle from the lateral direction changes, the decrease ordeterioration of the luminance can be restricted or inhibited.

Throughout this specification, the term “sheet” is used without regardto thickness, thus meaning a film as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic exploded perspective view showing an embodiment ofthe plane or flat light source unit and the display apparatus of thepresent invention.

FIG. 2 is a conceptual view illustrating the anisotropiclight-scattering property of the anisotropic scattering sheet shown inFIG. 1.

FIG. 3 is a schematic exploded perspective view showing an embodiment ofthe liquid crystal display apparatus comprising the plane light sourceunit of the present invention.

FIG. 4 is a schematic exploded perspective view showing anotherembodiment of the liquid crystal display apparatus comprising the planelight source unit of the present invention.

FIG. 5 is a schematic perspective view illustrating the method formeasurement of the intensity of scattered light.

FIG. 6 is a schematic view illustrating a method for measurement ofangle dependence on the luminance of the plane light source unit and atransmittable liquid crystal display apparatus comprising the lightsource unit.

FIG. 7 is a graph showing an intensity of scattered light as measuredwith the film according to Example 1.

FIG. 8 is a schematic cross-section view showing a conventionaltransmittable liquid crystal display apparatus.

FIG. 9 is a schematic cross-section view showing a backlight system foruse in a transmittable liquid crystal display apparatus.

FIG. 10 is a schematic perspective view of a tubular light source.

FIG. 11 is schematic cross-section view illustrating the emissiondistribution of the backlight system.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention shall now be described in detail with reference tothe attached drawings.

FIG. 1 shows a schematic exploded perspective view of an embodiment ofthe plane or flat light source unit and the display apparatus of thepresent invention. FIG. 2 is a conceptual view illustrating theanisotropic scattering property of the anisotropic scattering sheetshown in FIG. 1.

The above-mentioned display apparatus 1 comprises a liquid crystaldisplay unit (or liquid crystal display panel) 2 as a member to beilluminated which is composed of a liquid crystal cell having a liquidcrystal sealed therein, and a plane or flat light source unit 3 which isdisposed behind the display unit (or panel) and is used for illuminatingthe display unit 2.

The plane or flat light source unit 3 comprises a tubular light source 4such as a fluorescent tube (cold cathode tube), and a light guide member(light guide) 5 for being incident a light from the tubular light sourcefrom the lateral side thereof and emerging a light from a flat emergesurface. The light from the emerging surface of the light guide memberilluminates the display unit 2. Incidentally, the light guide member 5comprises a light-transmissive plate-like member, and the tubular lightsource 4 is disposed in almost parallel with and adjacent to the lateralside (or one side) of the light guide member. Furthermore, a reflectingmirror 6 b, for reflecting a light of the light source from the lateralside of the light guide member 5, is disposed at the outer lateral sideof the tubular light source 4, and a reflecting member or reflectinglayer 6 a, for reflecting a light from the tubular light source 4 to thefront or forward direction (the side of the display unit) to guide thelight to the display unit 2, is disposed on or at the back side of thelight guide member 5. That is, the plane or flat light source unitcomprises a reflector means, which are disposed on or at the lateralside and the back side of the light guide member 5, for reflecting thelight from the tubular light source 4 on the lateral side and theemerging side of the light guide member 5.

In such a plane or flat light source unit 3, the luminance distributionof a light emerged from the tubular light source 4 is not uniform andthe luminance distribution in the direction perpendicular to theaxis-direction of the tubular light source 4 is not uniform. Therefore,even when a light is emerged from the emerge surface through (via) thelight guide member 5, it is impossible to illuminate the display unit 2uniformly.

Therefore, according to the present invention, an anisotropic scatteringsheet 7 is disposed between the light guide member 5 and the displayunit (panel) 2 to illuminate the display unit 2 uniformly by a lightfrom the tubular light source 4. More specifically, as shown in FIG. 2for illustrating the relationship between an orientation of a dispersedphase particle and an anisotropic scattering property, the anisotropicscattering sheet 7 is composed of a continuous phase 10 and a dispersedphase 11 which differ in the refractive index (the refraction index)from each other. Each of the continuous phase 10 and the dispersed phase11 comprises a resin having high transparency. Moreover, the dispersedphase 11 dispersed in the continuous phase 10 has a mean aspect ratio oflarger than 1, and scatters an incident light in the direction ofadvance thereof. That is, the dispersed phase 11 can scatter atransmission light through a film strongly in the direction(Y-direction) perpendicular to the major direction (X-direction) of thedispersed phase particle.

More specifically, in the display apparatus, the anisotropic scatteringsheet 7 is disposed with addressing the major axis (X-axis) of thedispersed phase 11 to the longitudinal direction of the tubular lightsource 4 (axis-direction, X-direction). The Y-axial direction of thefilm is directed or oriented to the Y-axial direction perpendicular tothe longitudinal direction of the tubular light source 4. On the otherhand, a light from the tubular light source has uniform emissiondistribution in the X-axial direction but uneven emission distributionin the Y-axial direction. Moreover, in the case of utilizing theanisotropic scattering sheet 7, whereas the degree of scattering ofincident light is small in the direction of the major axis of thedispersed phase 11 (X-axial direction), the degree of scattering islarge in the direction perpendicular to the major axis (Y-axialdirection). Therefore, the light scattering characteristics Fx(θ) andFy(θ) show the relation of Fy(θ)>Fx(θ) as described below. Thus, thesheet scatters an incident light stronger in the Y-axial direction thanin the X-axial direction, and even when the tubular light source 4having uneven luminance distribution and anisotropy is used, thedeterioration of the luminance can be inhibited to illuminate thedisplay unit 2 uniformly. Furthermore, since the display unit 2 can beilluminated uniformly only by the intervention of the anisotropicscattering sheet 7, the structures of the plane or flat light sourceunit 3 and the display apparatus (particularly liquid crystal displayapparatus) 1 can be simplified, and the display data of the display unit2 can be visually recognized clearly or finely.

Incidentally, the scattering sheet may be provided with such acharacteristic or property as the scattering intensity shows the maximumin a certain scattering angle θ, that is, the scattering sheet hasdirectionality of the diffused light, as described below.

The plane or flat light source unit and the display apparatus of thepresent invention need only comprise at least one anisotropic scatteringsheet, and may comprise a plurality of anisotropic scattering sheets. Ifthe scattering sheet is disposed, it is unnecessary to align thelongitudinal or major direction of the dispersed phase particle (X-axialdirection of the film) to the longitudinal direction of the tubularlight source (X-axial direction) perfectly, and their directions may beshiftable each other as far as the emission distribution can beuniformalized. The angle between the longitudinal direction of thetubular light source and X-axial direction of the film is about 0 to20°, and usually about 0 to 10°.

In the case of using a plurality of anisotropic scattering sheets, thelongitudinal or major direction of the dispersed phase of each films maybe the same or different. For example, the plurality of anisotropicscattering sheets may be disposed in such directions as they havedifferent light-scattering directionality (e.g., the major direction ofthe dispersed phase) from each other, or the plurality (in particular,two pieces) of anisotropic scattering sheets may be disposed withdirecting the major directions of the dispersed phases to a directionbeing perpendicular each other.

The anisotropic scattering sheet may essentially position between thelight guide member and the display unit (panel). For example, the sheetmay be laminated on the emerging surface (or the front side) of thelight guide member and/or the incident surface (or the back side) of thedisplay unit, or interposed (intervened) between the light guide memberand the display unit separately. Incidentally, in the display apparatus,the anisotropic scattering sheet may be disposed between the displayunit and an observer (e.g., the display surface or front side of thedisplay unit).

FIG. 3 is a schematic exploded perspective view showing anotherembodiment of the liquid crystal display apparatus comprising the planeor flat light source unit of the present invention. The same referenceletters or symbols as the unit shown in FIG. 1 are given to memberswhich have the same functions shown in FIG. 3.

According to the embodiment, in the liquid crystal display apparatus la,an isotropic scattering or diffusing sheet 17 a, and a prism sheet 18 ain which sectional triangular fine prisms are formed in parallel for agiven direction are arranged in that order on the emerge surface of thelight guide member 5. Therefore, a light from the tubular light source 4a is diffused isotropically by the isotropic scattering sheet 17 athrough the light guide member 5 to be uniformly, and focused in frontby the prism sheet 18 a, as a result, the luminance can be improved toilluminate the display unit 2 from the back or reverse side. Moreover,when it is assumed that the axis-direction of the tubular light source 4is X-axial direction, since an anisotropic scattering sheet 19 a, forscattering a light anisotropically, is disposed with addressing the mainlight-scattering direction to Y-axial direction on the prism sheet 18 a,the light focused by the prism sheet 18 a is mainly scattered in theY-axial direction anisotropically rather than in the X-axial direction.

According to the display apparatus having such a structure, the angledependence of the luminance can be greatly reduced in the Y-axialdirection of the display surface. More specifically, as shown in FIG. 2,the anisotropic scattering sheet 19 a strongly scatters the transmittedlight through the sheet in the direction (Y-axial direction)perpendicular to the longitudinal or major direction of the dispersedphase particle (X-axial direction). Therefore, when the major directionof the dispersed phase of the anisotropic scattering sheet 19 a (X-axialdirection) is addressed to the vertical direction on the displaysurface, the sheet scatters a light in the horizontal direction (Y-axialdirection) strongly, the deterioration of the luminance can besuppressed even when an angle relative to the horizontal direction onthe display surface varies significantly, and the display on the displaysurface can be visually recognized clearly.

Furthermore, by using the anisotropic scattering sheet 19 a, the displayunit 2 is illuminated uniformly by a light from the tubular light source4 a, and even when the visual angle on the display surface of thedisplay unit 2 is wider, the display can be recognized visually with thehigh luminance. That is, as mentioned above, the anisotropic scatteringsheet 19 a can diffuse an incident light more strongly in the Y-axialdirection than in the X-axial direction, and even when the tubular lightsource 4 a having uneven luminance distribution and anisotropy is used,the deterioration of the luminance can be inhibited and the display unit2 can be illuminated uniformly. Furthermore, since the display unit 2can be illuminated uniformly only by the intervention of the anisotropicscattering sheet 19 a, the structures of the plane or flat light sourceunit 3 a and the display apparatus (particularly liquid crystal displayapparatus) 1 a can be simplified, and the display data on the displayunit 2 can be visually recognized clearly.

FIG. 4 is a schematic exploded perspective view showing still anotherembodiment of the liquid crystal display apparatus comprising the planeor flat light source unit of the present invention.

According to the embodiment, a plane or flat light source unit 3 b of aliquid crystal display apparatus 1 b comprises a light guide member 5,and an isotropic scattering or diffusing sheet 17 b and a prism sheet 18b which are arranged in that order on the emerging surface of the lightguide member, as similar to FIG. 3. Moreover, when it is assumed thatthe axis-direction of the tubular light source 4 b is X-axial direction,an anisotropic scattering sheet 19 b for scattering a lightanisotropically is disposed on the prism sheet 18 b with directing themain light-scattering direction to the horizontal direction of thedisplay unit 2 (X-axial direction). The anisotropic scattering sheet 19b mainly scatters a light focused by the prism sheet 18 banisotropically to the horizontal direction of the display unit 2(X-axial direction) rather than to the vertical direction thereof(Y-axial direction).

According to the display apparatus having such a structure, even whenthe tubular light source 4 b having uneven luminance distribution andanisotropy is used, the anisotropic scattering sheet 19 b scatters alight transmitted through the sheet strongly to the direction (X-axialdirection) perpendicular to the longitudinal or major direction of thedispersed phase particle (Y-direction). Therefore, the angle dependenceof the luminance can be reduced remarkably in the horizontal directionof the display surface (X-direction), and the display unit 2 can beilluminated uniformly and the display on the display surface can bevisually recognized clearly.

Incidentally, the isotropic diffusing sheet, the prism sheet and theanisotropic scattering sheet are interposed essentially between thelight guide member and the display unit. The disposing order of theisotropic diffusing sheet, the prism sheet and the anisotropicscattering sheet is not restricted. That is, the anisotropic scatteringsheet may be disposed between the light guide member and the displayunit. The anisotropic scattering sheet may be disposed or laminated(formed) on any surface of members, for instance, the emerging surface(or the front side) of the light guide of the backlight, the diffusingsheet surface, the prism sheet surface, or the incident surface (or theback surface) of the display unit. The anisotropic scattering sheet maybe interposed (intervened) between the light guide member and thedisplay unit separately. The anisotropic scattering sheet is usuallydisposed on or at the front side of the prism sheet, and preferablydisposed or laminated (formed) on the prism sheet. Such a arrangementenables to restrict the deterioration of the luminance at an angle ofgiven direction (in particular, the luminance in one direction) on thedisplay surface of a transmittable liquid crystal display apparatus.Moreover, in the case of disposing the anisotropic scattering sheet onthe prism sheet, the anisotropic scattering sheet can also function orserve as a protective film for the sensitive prism sheet with economicaladvantages.

The direction to be disposed of the anisotropic scattering sheet is notparticularly limited, and the sheet can be disposed toward a suitabledirection on the display surface of the display unit, for example, adirection in which a main scattering direction is oriented to thevertical direction of the display surface, the horizontal or lateraldirection thereof or the inclined direction thereof. According to thepreferred plane or flat light source unit, when it is assumed that theaxis-direction of the tubular light source is X-axial direction, theanisotropic scattering sheet is disposed with addressing a mainlight-scattering direction to the Y-axial direction of the tubular lightsource. In the preferred display apparatus, the anisotropic scatteringsheet is disposed toward the horizontal or lateral direction of thedisplay surface of the display unit.

Incidentally, the isotropic diffusing sheet may comprise a continuousphase having high transparency, and a dispersed phase dispersed in thecontinuous phase having the mean aspect ratio of about 1 and differingfrom the continuous phase in the refractive index. The continuous phasemay be formed with a transparent resin or a glass. The dispersed phasemay be formed with a transparent resin or an air bubble. The isotropicdiffusing sheet is preferably interposed (intervened) between the lightguide member and the prism sheet. If necessary, the isotropic diffusingsheet may be interposed (intervened) between the prism sheet and theanisotropic scattering sheet.

Moreover, the structure (or conformation) of the prism sheet is notparticularly restricted, and may comprise a sheet obtained by formingvarious structure or conformation, for example, uneven lines or rows (orprism lines or rows) composed of an uneven portion (convex portions orgroove portions), such as a triangle-shaped section, a trapezoid-shapedsection and a sinusoidal-shaped section, on the front and/or back sideof a substrate sheet, or comprises a sheet having regularly or randomlyscattered uneven portions. The direction to be disposed of the prismsheet relative to the axis-direction (X-axial direction) of the tubularlight source is not particularly restricted, and the prism sheet may bedisposed so that the extended direction of the prism lines is orientedtoward the X-axial direction or the Y-axial direction. Moreover, ifnecessary, two pieces of prism sheets may be disposed so that theextended directions of the prism lines are oriented toward a crossingdirection each other (for example, each sheet disposed towardX-direction and Y-direction).

Furthermore, as the display unit, a variety of display panels can beutilized without limiting to a liquid crystal display unit. The liquidcrystal display unit may comprise not only a liquid layer but alsovarious optical members or elements such as a color filter, a polarizingplate (or a polarizing film) and a phase plate. For instance, as theabove-mentioned embodiment, the liquid crystal display unit may beformed by laminating a first polarizing film, a first glass substrate, afirst electrode on the glass substrate, a first alignment membrane onthe electrode, a liquid layer, a second alignment membrane, a secondelectrode, a color filter, a second glass substrate and a secondpolarizing film in that order.

Incidentally, the light guide member (light guide) has usually a flat orplane surface (emerging surface) in almost parallel with the displayunit. The surface of the reflective layer side may be sloped or inclineddownward so that the thickness of the side adjacent to the tubular lightsource may be larger. As the tubular light source, a fluorescent tube(cold cathode tube) is usually utilized. A single tubular light sourceor a plurality of the tubular lights may be used.

According to the transmittable liquid crystal display apparatuscomprising the plane or flat light source device, the deterioration ofthe luminance depending on the visual angle on the display surface(e.g., an angle of a given direction such as a horizontal direction) canbe inhibited. Usually, in the case where the transmittable liquidcrystal display apparatus is used in an office, a user often changes ormoves the angle of vision into the lateral direction (horizontaldirection) of a display surface thereof. Therefore, in the display unit,when the anisotropic scattering sheet is disposed with directing a mainscattering direction of the sheet to the lateral direction (orhorizontal direction), a plane or flat light source unit can suppressthe change of the luminance on the lateral or horizontal direction ofthe display surface. Thus, the apparatus can be improved workingefficiency of a user (so-called a worker) who utilizes a transmittableliquid crystal display apparatus on a daily life, and the fatigue of theworker can be reduced.

[Anisotropic Scattering Sheet]

The anisotropic scattering sheet is required to be a film which iscapable of scattering an incident light in the light-advancing directionand having strong scattering intensity in a given direction (e.g.,Y-axial direction) without showing isotropic scattering, and, inaddition, having stronger the scattering intensity in the scatteringangle than that in a scattering angle in the direction perpendicular tothe given direction (X-axial direction) even when the scattering anglein the given direction becomes larger.

In order to uniformalize the luminance distribution and reduce thedecrease of the luminance depending on the angle relative to the displaysurface, the preferred anisotropic scattering sheet scatters mainly anincident light in the direction of advance thereof and has ananisotropic light-scattering characteristic. Thus, in terms of thescattering characteristic F(θ) showing the relation between thescattering angle θ and the intensity of scattered light F, the sheetsatisfies the following relation formula (1), and preferably relationformula (2):F 1=Fy(θ)/Fx(θ)>2, preferably F 1>5(θ=4 to 30°)  (1)F 2 =Fy(θ)/Fx(θ)>5, preferably F 2>10(θ=2 to 30°)  (2)

wherein Fx(θ) represents the light-scattering characteristic in thedirection of the X-axis (e.g., longitudinal or the major direction ofthe dispersed phase) and Fy(θ) represents the light-scatteringcharacteristic in the direction of the Y-axis perpendicular to theX-axis (e.g., the minor direction of the dispersed phase).

The value of F1=Fy(θ)/Fx(θ) is usually about 5 to 500 (e.g., 10 to 500),preferably about 15 to 500 and more preferably about 50 to 500 (e.g. 100to 400), and such values apply not only to a scattering angle θ in therange of 4 to 30° but also to a scattering angle θ ranging 4 to 15°.

The value of F2=Fy(θ)/Fx(θ) is usually about 10 to 500 (e.g., 15 to 500)and preferably about 20 to 500 (e.g. 20 to 400), and such values applynot only to a scattering angle θ=4 to 30° but also to a scattering angleθ=4 to 15°.

The more preferred anisotropic scattering sheet has a light-scatteringcharacteristic Fy(θ) decreasing gradually with increasing a scatteringangle θ in a scattering angle θ ranging 0 to 30° (for example, 2 to30°), and satisfies the light-scattering characteristic represented bythe following relation:F 3 =Fy(0°)/Fy(30°)<200  (3)

The value or rate of F3=(0°)/Fy(30°) is usually not more than 150 (e.g.,about 10 to 150), preferably not more than 100 (e.g. about 10 to 100),and more preferably not more than 50 (e.g., about 15 to 50).

Incidentally, as described hereinbefore, Japanese Patent ApplicationLaid-Open No. 314522/1992 (JP-4-314522A) describes an anisotropiclight-scattering material comprising a transparent resin matrix and adispersed phase particle which is morphologically anisotropic and isuniformly dispersed in the matrix in a positional relation shifted in anorderly and mutually parallel manner, as a lenticular lens for theprojection television screen. However, as described in FIGS. 3 to 6 ofthe literature, when the light scattering characteristic (intensity)against the scattering angle θ on a plane perpendicular to the majoraxes of dispersed particles is represented by Fy(θ) and the lightscattering characteristic (intensity) against the scattering angle θ ona plane parallel to the major axes of dispersed particles is shown byFx(θ), the ratio of Fy(θ) relative to Fx(θ) at the scattering angleθ=4°, that it to say the value of (Fy(4°)/Fx(4°)), is equal to about 2,and the anisotropic scattering characteristic of the anisotropiclight-scattering material is insufficient.

If the anisotropy coefficient F1 expressed by Fy(θ)/Fx(θ) is not morethan 2 (particularly, not more than 5), no uniform surface emission canbe realized when the film is applied to a liquid crystal displayapparatus having a tubular projector means (light source).

As described hereinabove, the anisotropic scattering sheet having thelight-scattering characteristic scatters a light intensely or extremelyin Y-axial direction, assuming that axis direction of the tubular lightsource is X-axial direction. Therefore, in the case where theanisotropic scattering sheet is disposed with directing the majordirection of the dispersed phase therein toward the vertical direction,the sheet scatters a light effectively in the horizontal direction.Thus, even when an angle on the horizontal direction relative to thedisplay surface varies larger, the deterioration of the luminance can beinhibited and the display on the display surface can be visuallyrecognized clearly.

When the scattering characteristic in the ψ direction, which isintermediate between the X-axis and Y-axis directions, is written asFψ(θ) (where ψ represents the angle from the X-axis direction; theX-axis direction corresponds to ψ=0° and the Y-axis directioncorresponds to ψ=90°), the anisotropic scattering sheet need notnecessarily have an anisotropy insuring that Fψ(θ) (ψ≠90°) will beapproximately equal to Fx(θ) directly, but preferably Fψ(θ) (ψ≠90°) maybe close to Fx((θ). Such a film is capable of scattering light with highanisotropy.

The scattering characteristic F(θ) can be measured using an instrumentshown in FIG. 5. This instrument comprises a laser irradiating unit(Nihon Kogaku Eng., NEO-20MS) 21 for projecting a laser light to theanisotropic scattering sheet 9 and a detector 22 for quantitating theintensity of the laser light transmitted through the anisotropicscattering sheet 7. The laser light is emitted at an angle of 90° withrespect to (perpendicular to) the anisotropic scattering sheet 9 and theintensity of light diffused by the film (diffusion intensity) F isplotted against the diffusing angle θ, whereby the light-scatteringcharacteristic can be determined.

In the anisotropic scattering sheet, as the anisotropy of the lightscattering thereof is higher, the angle dependence of the scattering ina given direction can be lower, therefore, the angle dependence of theluminance can be also lower. In the anisotropic scattering sheet,assuming that the angle which is perpendicular to the display surface is0°, the luminance can be prevented from decreasing even at the angle ofnot less than 40°, over that of 20°, on the display surface.

Such a characteristic may be represented by a ratio of the luminance inthe angle (θ) relative to the front luminance on the display surface, orby a ratio of the luminances at two angles (θ). That is, the use of theplane or flat light source unit of the present invention makes the valueof the above-mentioned rate smaller. For instance, a ratio of the frontluminance (N(0°)) at the angle which is perpendicular to the displaysurface (θ=0°) relative to the luminance at the angle of 18° (N(18°)) orat the angle of 40° (N(40°)), and a ratio of the luminance at the angleof 18° (N(18°)) relative to that at the angle of 40° (N(40°)) can bemade smaller. For example, by disposing the anisotropic scattering sheeton a prism sheet of a liquid crystal display apparatus having aconventional structure, a transmittable liquid crystal display apparatuswhich is suitable for a business monitor satisfying (or meeting) TCO99standard can be provided.

The anisotropic scattering sheet comprises a continuous phase (such as aresin continuous phase) and a dispersed phase which is dispersed in thecontinuous phase (such as a particulate or fibrous dispersed phase). Thecontinuous phase and the dispersed phase are different from each otherin the refractive index, and are usually incompatible or hardlycompatible with each other. The continuous phase and the dispersed phasemay be usually formed with a transparent substance.

The resin for constituting the continuous phase and the dispersed phaseincludes thermoplastic resins [an olefinic resin, a halogen-containingresin (including a fluorine-containing resin), a vinyl alcohol-seriesresin, a vinyl ester-series resin, a (meth)acrylic resin, a styrenicresin, a polyester-series resin, a polyamide-series resin, apolycarbonate-series resin, a cellulose derivative, etc.] andthermosetting resins (an epoxy resin, an unsaturated polyester resin, adiallyl phthalate resin, a silicone resin, etc.). The preferred resinsare the thermoplastic resins.

The olefinic resin includes but is not limited to homo- or copolymers ofC₂₋₆olefins (ethylenic resins such as polyethylene, ethylene-propylenecopolymer, etc., polypropylene-series resins such as polypropylene,propylene-ethylene copolymer, propylene-butene copolymer, etc.,poly(methylpentene-1), propylene-methylpentene copolymer, etc.), andcopolymers of C₂₋₆olefins and copolymerizable monomers(ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylatecopolymer, etc.).

The halogen-containing resin includes but is not limited to vinylhalide-series resins (e.g. homopolymers of vinyl chloride orfluorine-containing monomers, such as polyvinyl chloride,polytetrafluoroethylene, polychlorotrifluoroethylene, poly(vinylfluoride), etc., copolymers of vinyl chloride or fluorine-containingmonomers, such as tetrafluoroethylene-hexafluoropropylene copolymer,tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, etc.; andcopolymers of vinyl chloride or fluorine-containing monomers and othercopolymerizable monomers, such as vinyl chloride-vinyl acetatecopolymer, vinyl chloride-(meth)acrylate copolymer,tetrafluoroethylene-ethylene copolymer, etc.), and vinylidenehalide-series resins (poly(vinylidene chloride), poly(vinylidenefluoride), copolymers of vinyl chloride or fluorine-containingvinylidene monomers and other monomers).

The derivative of vinyl alcohol-series resin includes polyvinyl alcohol,ethylene-vinyl alcohol copolymers, etc. The vinyl ester-series resinincludes homo- or copolymers of vinyl ester-series monomers (e.g.polyvinyl acetate), copolymers of vinyl ester-series monomers andcopolymerizable monomers (e.g. vinyl acetate-ethylene copolymer, vinylacetate-vinyl chloride copolymer, vinyl acetate-(meth)acrylatecopolymer, etc.).

The (meth)acrylic resin includes but is not limited topoly(meth)acrylates such as polymethyl(meth)acrylate, methylmethacrylate-(meth)acrylic acid copolymer, methylmethacrylate-(meth)acrylate-(meth)acrylic acid copolymers, methylmethacrylate-(meth)acrylate copolymers, and (meth)acrylate-styrenecopolymers (e.g., MS resin). The preferred (meth)acrylic resin includespoly(C₁₋₆alkyl (meth)acrylate) and methyl methacrylate-acrylatecopolymers.

The styrenic resin includes homo- or copolymers of styrenic monomers(e.g. polystyrene, styrene-α-methylstyrene copolymer, etc.), andcopolymers of styrenic monomers and copolymerizable monomers [e.g.styrene-acrylonitrile copolymer (AS resin), styrene-(meth)acrylic estercopolymers (such as styrene-methyl methacrylate copolymer),styrene-anhydrous maleic acid copolymer, etc.].

The polyester-series resin includes aromatic polyesters obtainable froman aromatic dicarboxylic acid, such as terephthalic acid, and analkylene glycol (homopolyesters, e.g. polyalkylene terephthalates suchas polyethylene terephthalate, polypropylene terephthalate, polybutyleneterephthalate, etc. and polyalkylene naphthalates such as polyethylenenaphthalate, polybutylene naphthalate, etc.; and copolyesters containingan alkylene arylate unit as a main component (e.g. not less than 50 mole%, preferably 75 to 100 mole %, more preferably 80 to 100 mole %)),aliphatic polyesters obtainable by using aliphatic dicarboxylic acidssuch as adipic acid, and liquid-crystalline polyesters.

The polyamide-series resin includes aliphatic polyamides such as nylon46, nylon 6, nylon 66, nylon 610, nylon 612, nylon 11, nylon 12, etc.and aromatic polyamides such as xylylenediamine adipate (MXD-6), amongothers. The polyamide-series resin is not restricted to homopolyamidesbut may be copolyamides.

The polycarbonate-series resin includes aromatic polycarbonates based onbisphenols (e.g. bisphenol A) and aliphatic polycarbonates such asdiethylene glycol bis-aryl carbonates.

The cellulose derivative includes cellulose esters (e.g. celluloseacetate, cellulose propionate, cellulose butyrate, cellulose phthalate,etc.), cellulose carbamates (e.g. cellulose phenylcarbamate), celluloseethers (e.g. alkylcelluloses, benzylcellulose, hydroxyalkylcelluloses,carboxymethylcellulose, cyanoethylcellulose, etc.).

Where necessary, the resin component may have been modified (e.g.rubber-modified).

It is also possible to form a continuous phase matrix from the resincomponent and graft- or block-copolymerize the dispersed phase componentwith this matrix resin. As examples of such polymer, there can bementioned rubber-block copolymers (e.g. styrene-butadiene copolymer (SBresin)) and rubber-grafted styrenic resins (e.g.acrylonitrile-butadiene-styrene copolymer (ABS resin)).

The fibrous dispersed phase includes organic fiber and inorganic fiber.The organic fiber includes heat-resistant organic fibers such as aramidfiber, fully aromatic polyester fiber, polyimide fiber, etc. Theinorganic fiber includes but is not limited to fibrous fillers (e.g.inorganic fibers such as glass fiber, silica fiber, alumina fiber,zirconia fiber, etc.) and flaky fillers (e.g. mica etc.).

The preferred component for making up the continuous phase or thedispersed phase (discontinuous phase or dispersed phase) includesolefinic resins, (meth)acrylic resins, styrenic resins, polyester-seriesresins, polyamide-series resins and polycarbonate-series resins, amongothers. Moreover, the resin constituting the continuous phase and/ordispersed phase may be crystalline or noncrystalline, and the continuousphase and dispersed phase may be formed using noncrystalline resins. Inthe preferred embodiment, a crystalline resin and a noncrystalline resincan be used in combination. Thus, either one (for example, thecontinuous phase) of the continuous phase and dispersed phase(discontinuous phase) may be made of a crystalline resin and the otherone (for example, dispersed phase) of the phases be made of anoncrystalline resin.

The crystalline resin which can be used includes olefinic resins(polypropylene-series resin with a propylene content of not less than 90mole %, such as polypropylene, propylene-ethylene copolymer, etc.,poly(methylpentene-1), etc.), vinylidene-series resins (e.g. vinylidenechloride-series resin), aromatic polyester-series resins (e.g.polyalkylene arylate homopolyesters such as polyalkylene terephthalates,polyalkylene naphthalates, etc., copolyesters containing not less than80 mole % of an alkylene arylate unit, liquid-crystalline aromaticpolyesters, etc.), and polyamide-series resins (e.g. aliphaticpolyesters having short-chain segments, such as nylon 46, nylon 6, nylon66, etc.). These crystalline resins can be used independently or in acombination of two or more species.

The degree of crystallization of the crystalline resin (e.g. acrystalline polypropylene-series resin) may for example be about 10 to80%, preferably about 20 to 70%, and more preferably about 30 to 60%.

As the resin constituting the continuous phase, usually a highlytransparent resin, in particular a highly transparent and highlyheat-resistant transparent resin, is used. The preferred continuousphase-forming resin is a crystalline resin having high fluidity as amolten property. The combination of such a resin and the dispersedphase-forming resin contributes to a homogeneous (uniform) compoundingwith the dispersed phase and improves homogeneity of the compound(uniform dispersability of the dispersed phase). When a resin having ahigh melting point or glass transition point (particularly a crystallineresin having a high melting point) is used as the continuousphase-forming resin, its high heat stability and good film-formingproperties improve a drawing ratio and the film-formation in amelt-molding process. Therefore, the orientation treatment (or monoaxialstretching) to improve the anisotropic scattering characteristic can becarried out at a comparatively high temperature (e.g. about 130 to 150°C.), the processing can be carried out readily, and the dispersed phasecan be orientated easily. Furthermore, the film is stable over a broadtemperature range (e.g. room temperature to about 80° C.) so that it canbe utilized as a component part of a display apparatus or device (liquidcrystalline display apparatus or device) with advantage. In addition,crystalline resins (e.g. a crystalline polypropylene resin) aregenerally inexpensive. The preferred crystalline resin includes acrystalline polypropylene-series resin which is inexpensive and has highheat stability.

The resin constituting the continuous phase may be a resin having amelting point or glass transition temperature of about 130 to 280° C.,preferably about 140 to 270° C., and more preferably about 150 to 260°C.

The noncrystalline resin includes but is not limited to vinyl-seriespolymers (homo- or copolymers of vinyl-series monomers such as ionomers,ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic estercopolymers, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer,poly(vinyl acetate), vinyl alcohol-series resin, etc.), (meth)acrylicresins (e.g. poly(methyl methacrylate), methyl methacrylate-styrenecopolymer (MS resin), etc.), styrenic resins (polystyrene, AS resin,styrene-methyl methacrylate copolymer, etc.), polycarbonate-seriespolymers, noncrystalline polyester-series resins (aliphatic polyesters,polyalkylene arylate copolyesters whose diol component and/or aromaticdicarboxylic acid component has been partially substituted, polyarylateresins, etc.), polyamide-series resins (e.g. aliphatic polyamides havinglong-chain segments and noncrystalline aromatic polyamides), andthermoplastic elastomers (e.g. polyester elastomers, polyolefinelastomers, polyamide elastomers, styrenic elastomers, etc.). Referringto the noncrystalline polyester-series resins, the polyalkylene arylatecopolyester includes copolyesters obtainable by using at least onemember selected from (poly)oxyalkylene glycol (e.g. diethylene glycol,triethylene glycol), cyclohexanedimethanol, phthalic acid, isophthalicacid and aliphatic dicarboxylic acids (e.g. adipic acid) as part (e.g.about 10 to 80 mole %, preferably about 20 to 80 mole %, and morepreferably about 30 to 75 mole %) of the diol component (C₂₋₄alkyleneglycol) and/or aromatic dicarboxylic acid component (terephthalic acid,naphthalenedicarboxylic acid). These noncrystalline resins can be usedindependently or in a combination of two or more species.

As the resin constituting the dispersed phase, a resin being highlytransparent, deforming easily at an orientation treatment temperaturesuch as a monoaxial stretching temperature and having practical heatstability is usually employed. In particular, when a resin having alower melting point or glass transition temperature (or point) than thecontinuous phase (particularly a noncrystalline resin having a lowermelting point or glass transition temperature than a crystalline resin)is used as the resin constituting the dispersed phase, the aspect ratioof dispersed phase particles can be easily increased by an orientationtreatment such as monoaxial stretching. Incidentally, the melting pointor glass transition temperature of the dispersed phase-forming resin islower than that of the resin constituting the continuous phase in manyinstances, and may for example be about 50 to 180° C., preferably about60 to 170° C., and more preferably about 70 to 150° C.

Among the noncrystalline resins constituting the dispersed phase, atleast one resin selected from a noncrystalline copolyester-series resinand a polystyrenic resin is preferred. When the noncrystallinecopolyester is used to form the dispersed phase, not only a high degreeof transparency can be assured but the glass transition temperature canbe about 80° C. so that a deformation can be readily introduced to thedispersed phase at the temperature used for orientation treatment suchas monoaxial stretching and the dispersed phase can be kept stable overa given temperature range (for example, room temperature to about 80°C.) after molding. Moreover, the noncrystalline copolyester (e.g. apolyethylene terephthalate copolyester obtainable by using a diolcomponent such as ethyleneglycol/cyclohexanedimethanol=about 10/90 to60/40 (mole %), preferably about 25/75 to 50/50 (mole %)) has a highindex of refraction (e.g. about 1.57) so that the refractive indexdifferential from the continuous phase can be increased. In addition,the noncrystalline copolymer may be compounded with the crystallineresin (such as polypropylene-series resin) effectively.

Since the polystyrenic resin has the high refractive index and the hightransparency, and has such a high glass transition temperature as about100 to 130° C., an anisotropic scattering sheet having excellentheat-resistance can be prepared by using the resin. Moreover, thepreferred anisotropic scattering sheet can be prepared by using aninexpensive polystyrenic resin at a comparative small amount relative tothe crystalline resin as the continuous phase (e.g.,polypropylene-series resin), in addition, at comparative low drawingratio. Furthermore, the sheet shows extremely high anisotropy in thecase of being subjected to calendering after melt molding.

The combination of the crystalline resin forming the continuous phasewith the noncrystalline resin forming the dispersed phase includes, forexample, the combination of a crystalline polyolefinic resin (e.g. acrystalline polypropylene resin) with at least one member selected fromnoncrystalline polyesters (e.g., polyalkylene arylate copolyesters suchas polyalkylene terephthalate copolyesters) and polystyrenic resins.

The continuous phase and dispersed phase (discontinuous phase ordispersoid) are constituted of components differing from each other inthe index of refraction. By using components differing in the index ofrefraction, the film can be provided with light-diffusing properties.The refractive index differential between the continuous phase and thedispersed phase may for example be not less than 0.001 (e.g. about 0.001to 0.3), preferably about 0.01 to 0.3, and more preferably about 0.01 to0.1.

As the combination of resins giving such a defined refractive indexdifferential, the following combinations may be mentioned by way ofexample.

-   (1) The combination of an olefinic resin (particularly a    propylene-series resin) with at least one member selected from the    group consisting of an acrylic resin, a styrenic resin, a    polyester-series resin, a polyamide-series resin and a    polycarbonate-series resin.-   (2) The combination of a styrenic resin with at least one member    selected from the group consisting of a polyester-series resin, a    polyamide-series resin and a polycarbonate-series resin.-   (3) The combination of a polyester-series resin with at least one    member selected from the group consisting of a polyamide-series    resin and a polycarbonate-series resin.

The anisotropic scattering sheet may contain a compatibilizing agentwhere necessary. With a compatibilizing agent, the miscibility andmutual affinity of the continuous and dispersed phases can be improved,the formation of defects (voids and other defects) on orientation of thefilm can be prevented, and the loss of transparency of the film can beprevented. Furthermore, the adhesion between the continuous phase andthe dispersed phase can be enhanced so that even when the film isstretched monoaxially, the adhesion of the dispersed phase on thestretching equipment can be decreased.

The compatibilizing agent can be selected from the conventionalcompatibilizing agents according to the species of continuous anddispersed phases and, for example, modified resins as modified withoxazoline compounds or modifying groups (carboxyl, acid anhydride,epoxy, oxazolinyl and other groups), diene-series copolymers (random andother copolymers) obtainable by copolymerization with diene orrubber-containing polymers [e.g. homo- or copolymers of diene-seriesmonomers or copolymerizable monomers (aromatic vinyl monomers etc.);diene-series graft copolymers such as acrylonitrile-butadiene-styrenecopolymer (ABS resin); diene-series block copolymers such asstyrene-butadiene (SB) block copolymer, hydrogenated styrene-butadiene(SB) block copolymer, hydrogenated styrene-butadiene-styrene blockcopolymer (SEBS), hydrogenated (styrene-ethylene/butylene-styrene) blockcopolymer, etc. and their hydrogenation versions etc.], and diene orrubber-containing polymers modified with the modifying groups (epoxy andother groups). These compatibilizing agents can be used independently orin a combination of two or more species.

As the compatibilizing agent, polymers (a random, block or graftcopolymer) having the same components as, or components in common with,the polymer blend constituent resins, or polymers (random, block orgraft copolymers) having an affinity for the polymer blend constituentresins are usually employed.

The diene-series monomer includes conjugated dienes such as C₄₋₂₀conjugated dienes which may optionally be substituted, e.g. butadiene,isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, piperylene,3-butyl-1,3-octadiene, phenyl-1,3-butadiene, etc. The conjugated dienescan be used independently or in a combination of two or more species.Among these conjugated dienes, butadiene and isoprene are preferred.

The aromatic vinyl monomer includes but is not limited to styrene,a-methylstyrene, vinyltoluenes (p-methylstyrene etc.), p-t-butylstyrene,divinylbenzenes and 1,1-diphenylstyrene. Among these aromatic vinylmonomers, styrene is preferred. The (meth)acrylic monomer includes alkyl(meth)acrylates [e.g. methyl (meth)acrylate] and (meth)acrylonitrile,among others. As the maleimide-series monomer, maleimide,N-alkylmaleimides, N-phenylmaleimide, etc. can be mentioned. Thesemonomers can be used independently or in a suitable combination of twoor more species.

The modification mentioned above can be made by copolymerizing a monomercorresponding to the modifying group (e.g. a carboxyl group-containingmonomer such as (meth)acrylic acid for carboxyl-modification, maleicanhydride for acid anhydride-modification, a (meth)acrylic monomer forester-modification, a maleimide-series monomer formaleimide-modification, and an epoxy group-containing monomer such asglycidyl (meth)acrylate for epoxy-modification). The epoxy-modificationmay be made by epoxidization of an unsaturated double bond.

The preferred compatibilizing agent is an unmodified or modifieddiene-series copolymer, particularly a modified block copolymer (e.g. anepoxidized diene-series block copolymer or an epoxy-modifieddiene-series block copolymer such as epoxidizedstyrene-butadiene-styrene (SBS) block copolymer). The epoxidizeddiene-series block copolymer is not only highly transparent but has acomparatively high softening point of about 70° C., and is capable ofcompatibilizing resins in many combinations of continuous and dispersedphases to disperse the dispersed phase uniformly.

The block copolymer mentioned above can be constituted of a conjugateddiene block or the corresponding partially hydrogenated block and anaromatic vinyl block. In the epoxidized diene-series block copolymer,the double bonds in the conjugated diene blocks may have been partly orcompletely epoxidized.

The ratio (weight ratio) of the aromatic vinyl block relative to theconjugated diene block (or the corresponding hydrogenated block)[former/latter] may for example be about 5/95 to 80/20 (e.g. about 25/75to 80/20), more preferably about 10/90 to 70/30 (e.g. about 30/70 to70/30), and usually about 50/50 to 80/20.

The number average molecular weight of the block copolymer can beselected from the range of, for example, about 5,000 to 1,000,000,preferably about 7,000 to 900,000, and still more preferably about10,000 to 800,000. The molecular weight distribution [the ratio [Mw/Mn]of weight average molecular weight (Mw) relative to number averagemolecular weight (Mn)] may for example be not more than 10 (about 1 to10), and preferably about 1 to 5.

The molecular structure of the block copolymer may be linear (straight),branched, radial or any combination thereof. The block structure of theblock copolymer may for example be a monoblock structure, a multiblockstructure such as a tereblock structure, a trichain-radial tereblockstructure or tetrachain-radial tereblock structure. Such blockstructures may for example be written as X-Y, X-Y-X, Y-X-Y, Y-X-Y-X,X-Y-X-Y, X-Y-X-Y-X, Y-X-Y-X-Y, (X-Y-)₄Si, (Y-X-)₄Si, etc. where Xrepresents an aromatic diene block and Y represents a conjugated dieneblock.

The ratio of epoxy groups in the epoxidized diene-series block copolymeris not particularly restricted but, in terms of oxygen concentration ofoxirane, may for example be about 0.1 to 8 weight %, preferably about0.5 to 6 weight %, and more preferably about 1 to 5 weight %. The epoxyequivalent (JIS K7236) of the epoxidized block copolymer may for examplebe about 300 to 1,000, preferably about 500 to 900, more preferablyabout 600 to 800.

The epoxidized block copolymer (e.g. epoxidized SBS block copolymer)making up the compatibilizing agent is not only highly transparent butalso has a comparatively high softening point (about 70° C.), and iscapable of effectively compatibilizing resins in many combinations ofcontinuous and dispersed phases to disperse the dispersed phase resinuniformly. Moreover, the epoxidized block copolymer with an aromaticvinyl block (e.g. styrene block) content of about 60 to 80 weight % hasa refractive index which is comparatively high (e.g. about 1.57) andclose to the refractive index of the dispersoid resin (e.g. anoncrystalline copolyester) so that the dispersoid resin can be causedto be uniformly dispersed while the light scattering performance of thedispersoid resin is maintained.

The refractive index of the compatibilizing agent (e.g. epoxidized blockcopolymer) may be approximately the same as that of the dispersoid resin(for example, the difference from the refractive index of dispersoidresin is about 0 to 0.01, and preferably about 0 to 0.005).

The epoxidized block copolymer mentioned above can be produced byepoxidizing a diene-series block copolymer (or a partially hydrogenatedblock copolymer) which has been prepared by the conventional method. Theblock copolymer can for example be prepared by polymerizing an aromaticvinyl monomer with a diene-series monomer in the presence of a lithiumcatalyst in an inert solvent [Japanese Patent Publication No. 23798/1965(JP-40-23798B), Japanese Patent Publication No. 3252/1972 (JP-47-3252B),Japanese Patent Publication No. 2423/1973 (JP-48-2423B), Japanese PatentApplication Laid-Open No. 33184/1976 (JP-51-33184A), Japanese PatentPublication No. 32415/1971 (JP-46-32415B), Japanese Patent ApplicationLaid-Open No. 166518/1984 (JP-59-166518A), Japanese Patent PublicationNo. 36957/1974 (JP-49-36957B), Japanese Patent Publication No.17979/1968 (JP-43-17979B), Japanese Patent Publication No. 32415/1971(JP-46-32415B), Japanese Patent Publication No. 28925/1981(JP-56-28925B), etc.]. The hydrogenated block copolymer may for examplebe prepared by hydrogenating a block copolymer with the aid of ahydrogenation catalyst in an inert solvent [Japanese Patent PublicationNo. 8704/1967 (JP-42-8704B), Japanese Patent Publication No. 6636/1968(JP-43-6636B), Japanese Patent Application Laid-Open No. 133203/1984(JP-59-133203A), etc.].

The epoxidization can be carried out in accordance with the conventionalepoxidizing method, for example by epoxidizing the above-mentioned blockcopolymer with an epoxidizing agent (e.g. a peracid, a hydroperoxide,etc.) in an inert solvent. The peracid mentioned just above includesperformic acid, peracetic acid, trifluoroperacetic acid, perbenzoicacid, etc. The hydroperoxide includes inorganic hydroperoxides (e.g.hydrogen peroxide) and organic hydroperoxides (e.g. t-butylhydroperoxide). The hydroperoxide is used in combination with an acid ora metal catalyst in many cases, and the combination of tungsticacid-sodium hydroxide mixture with hydrogen peroxide, the combination ofan organic acid with hydrogen peroxide, and the combination ofmolybdenum hexacarbonyl with t-butyl hydroperoxide can be mentioned asexamples. The amount (level) to be used of the epoxidizing agent is notparticularly restricted but can be broadly and judiciously selectedaccording to the kind of block copolymer, the kind of epoxidizing agent,and expected degree of epoxidization (e.g. epoxy equivalent). Theisolation and purification of the epoxidized diene-series blockcopolymer can be carried out by a suitable method, for example themethod which comprises precipitating the copolymer with a poor solvent,the method which comprises adding the copolymer to hot water understirring and removing the solvent by distillation, or the directdesolventization method (direct desolvation method).

The amount (level) to be used of the compatibilizing agent may beselected from the range of, for example, about 0.1 to 20 weight %,preferably about 0.5 to 15 weight %, and more preferably about 1 to 10weight %, based on the total resin composition.

In the anisotropic scattering sheet, the preferred combination ofcontinuous phase, dispersed phase and compatibilizing agent includes thecombination of a continuous phase composed of a resin having hightransparency and high thermal stability (e.g. a crystalline resin suchas a crystalline polypropylene-series resin), a dispersed phase composedof a resin having high transparency, good thermal deformability and afair degree of thermal stability (e.g. a noncrystalline (amorphous)resin such as a noncrystalline copolyester, a polystyrenic resin) and acompatibilizing agent comprising an epoxidized block copolymer.

In the anisotropic scattering sheet, the ratio of the continuous phaserelative to the dispersed phase can be judiciously selected from therange of, for example, [former/latter (by weight)]=about 99/1 to 30/70(e.g., about 95/5 to 40/60), preferably about 99/1 to 50/50 (e.g., about95/5 to 50/50), and more preferably about 99/1 to 75/25, with referenceto the kinds, melt viscosity and light diffusing properties of theresins.

In the preferred anisotropic scattering sheet, the relative amount ofthe continuous phase, dispersed phase and compatibilizing agent may forexample be as follows.

-   (1) continuous phase/dispersed phase (weight ratio)=about 99/1 to    50/50, preferably about 98/2 to 60/40, more preferably about 90/10    to 60/40, and particularly about 80/20 to 60/40.-   (2) dispersed phase/compatibilizing agent (weight ratio)=about 99/1    to 50/50, preferably about 99/1 to 70/30, and more preferably about    98/2 to 80/20.

When the components are used in such ratios, the dispersed phase can beuniformly dispersed even if pellets of each components are directlymelt-kneaded together without compounding the components in advance but,with avoiding the formation of voids on orientation treatment, e.g.monoaxial stretching, and a light-scattering film of high transmittancecan be obtained.

More specifically, for example, the following resin composition can becompounded readily, and the melt-molding can be carried out withcompounding the raw materials only by feeding them, and the formation ofvoids can be prevented even when monoaxial stretching is carried out, asa result, an anisotropic diffusing film having high transmissivity canbe obtained:

-   (a) a resin composition comprising a crystalline    polypropylene-series resin as the continuous phase, a noncrystalline    copolyester-series resin as the dispersed phase, and an epoxidized    SBS (styrene-butadiene-styrene block copolymer) as the    compatibilizing agent, in which a ratio of the continuous phase    relative to the dispersed phase is 99/1 to 50/50 (particularly,    80/20 to 60/40) (weight ratio) and a ratio of the dispersed phase    relative to the compatibilizing agent is 99/1 to 50/50    (particularly, 98/2 to 80/20) (weight ratio);-   (b) a resin composition comprising a crystalline    polypropylene-series resin as the continuous phase, a polystyrenic    resin as the dispersed phase, and an epoxidized SBS as the    compatibilizing agent, in which a ratio of the continuous phase    relative to the dispersed phase is 99/1 to 50/50 (particularly,    90/10 to 70/30) (weight ratio) and a ratio of the dispersed phase    relative to the compatibilizing agent is 99/1 to 50/50    (particularly, 99.5/0.5 to 90/10) (weight ratio).

In the anisotropic scattering sheet, particles forming the dispersedphase are each so configured that the ratio of the mean dimension L ofthe longitudinal or major axis to the mean dimension W of the minor axis(mean aspect ratio, L/W) is larger than 1 and the direction of the majoraxis of each particle coincides with the x-axis of the film. Thepreferred mean aspect ratio (L/W) may for example be about 2 to 1000,preferably about 5 to 1000, more preferably about 5 to 500 (e.g., 20 to500), and usually about 50 to 500 (particularly 70 to 300). Themorphology of dispersed phase particles may for example be afootball-like (e.g. spheroidal), filamentous or cuboid. The larger theaspect ratio is, the higher is the anisotropy expressed in thescattering of light.

The mean dimension L of the major axis of the dispersed phase particlemay for example be about 0.1 to 200 μm (e.g., about 1 to 100 μm),preferably about 1 to 150 μm (e.g., about 1 to 80 μm), particularlyabout 2 to 100 μm (e.g., about 2 to 50 μm), and usually about 10 to 100μm (e.g., about 30 to 100 μm, particularly about 10 to 50 μm). The meandimension W of the minor axis of the dispersed phase particle may forexample be about 0.1 to 10 μm, preferably about 0.15 to 5 μm (e.g.,about 0.5 to 5 μm), and more preferably about 0.2 to 2 μm (e.g., about0.5 to 2 μn). The mean dimension W of the minor axis of the dispersedphase particle may for example be about 0.01 to 0.5 μm, preferably about0.05 to 0.5 μm, and more preferably about 0.1 to 0.4 μm.

The orientation coefficient of dispersed phase particles may for examplebe not less than 0.7 (e.g., about 0.7 to 1), preferably about 0.8 to 1,and more preferably about 0.9 to 1. The higher the orientationcoefficient is, the higher is the anisotropy imparted to scatteredlight.

The orientation coefficient can be calculated by means of the followingequation.Orientation coefficient=(3<cos² θ>−1)/2where θ represents the angle between the major axis of the particulatedispersed phase and the X-axis of the film or sheet (when the major axisis parallel to the X-axis, θ=0°); <cos² θ> represents the average ofcos² θ values found for individual dispersed phase particles and can beexpressed as follows.<cos² θ>=∫n(θ)·cos² θ·dθ(wherein n(θ) represents the percentage (weight percent) of dispersedphase particles having the angle θ in the total population of dispersedphase particles.)

Incidentally, the anisotropic scattering sheet may be provided withdirectionality of the diffused or scattered light. That a film hasdirectionality means that, among the angles of intense scattering inanisotropic diffusion, there is an angle giving a maximum scatteringintensity when the diffused light has directionality. Referring to themeasuring system depicted in FIG. 5, when the diffused light intensity Fis plotted against the diffusion angle θ, the curve of plots has amaximum or a shoulder (especially an inflection point such as a maximum)within a given range of diffusion angle θ (angles excluding θ=0°) whenthe diffused light has directionality.

For imparting the directionality to the anisotropic scattering sheet,the refractive index differential between the continuous phase matrixresin and the dispersed phase particles may for example be about 0.005to 0.2, preferably about 0.01 to 0.1, and the mean dimension of themajor axes of the dispersed phase particles may for example be about 1to 100 μm, preferably about 5 to 50 μm. The aspect ratio may for examplebe about 10 to 300 (e.g., 20 to 300) and preferably about 50 to 200, andmay be about 40 to 300.

The anisotropic scattering sheet may contain the conventional additives,for example stabilizers such as an antioxidant, an ultraviolet absorber,a heat stabilizer, etc.; a plasticizer, an antistatic agent, a flameretardant and a filler.

The thickness of the anisotropic scattering sheet is about 3 to 300 μm,preferably about 5 to 200 μm (e.g., about 30 to 200 μm), and morepreferably about 5 to 100 μm (e.g., about 50 to 100 μm). Moreover, thetotal light transmittance of the anisotropic scattering sheet may forexample be not less than 85% (85 to 100%), preferably about 90 to 100%,and more preferably about 90 to 95%.

Incidentally, the anisotropic scattering sheet may be a monolayered filmcomprising an anisotropic scattering layer singly, or may be a laminatedfilm in which a transparent resin layer is laminated on at least oneside (particularly, both sides) of the anisotropic scattering layer.When the anisotropic scattering layer is protected by the transparentresin layer, the dispersed phase particle can be prevented from fallingout or sticking to improve flaw or scratch resistance of the film orstability in the film-producing process, and strength or handling of thefilm can be improved.

The resin constituting the transparent resin layer can be selected fromthe resins exemplified as the resins constituting the continuous phaseor the dispersed phase. It is preferred that the transparent resin layeris composed of the same kind of resins (in particular, the same resin)as one constituting the continuous phase.

The preferred transparent resin for enhancing heat resistance orblocking resistance includes a resin having heat resistance (e.g. aresin having high glass transition temperature or melting point), acrystalline resin and the like. The glass transition temperature ormelting point of the resin constituting the transparent resin layer maybe the same degree as that of the resin constituting the continuousphase, and may be, for example, about 130 to 280° C., preferably about140 to 270° C., and more preferably about 150 to 260° C.

The thickness of the transparent resin layer may for example be similarto that of the anisotropic scattering sheet. In particular, when thethickness of the anisotropic light-scattering layer is about 3 to 300μm, the thickness of the transparent resin layer can be selected fromthe range of about 3 to 150 μm.

The thickness ratio of the anisotropic scattering layer relative to thetransparent resin layer may, for example, be the anisotropic scatteringlayer/the transparent resin layer=about 5/95 to 99/1, preferably about50/50 to 99/1, and more preferably about 70/30 to 95/5. The thickness ofthe laminated film is, for example, about 6 to 600 μm, preferably about10 to 400 μm, and more preferably about 20 to 250 μm.

On the surface of the anisotropic scattering sheet, the releasing agentsuch as silicone oil may be applied or the treatment by corona dischargemay be given or applied, as far as the optical properties of the film isnot deteriorated.

Incidentally, the anisotropic scattering sheet may be formed withsurface irregularities (or concave-convex sites) extending along X-axialdirection of the film (the major direction of the dispersed phase). Theformation of such surface irregularities imparts a higher degree ofanisotropy to the film.

[Process for Producing the Anisotropic Scattering Sheet]

The anisotropic scattering sheet can be obtained by dispersing andorienting a dispersed phase-forming component (resin component, fibrouscomponent, etc.) in a continuous phase-forming resin. For example, thedispersoid component can be dispersed by the method which comprisesblending the continuous phase-forming resin with the dispersoid-formingcomponent (resin component, fibrous component, etc.) in the conventionalmanner (e.g. melt-blending method, tumbler method, etc.) wherenecessary, melt-mixing them, and extruding the molten mixture from aT-die, a ring die, or the like into a film form. The orientation of thedispersed phase can be achieved by, for example, (1) the methodcomprising drafting (or drawing) the extruded sheet to form the sheet inthe course of extrusion, (2) the method comprising stretching theextruded sheet monoaxially, or (3) a combination of the methods (1) and(2). The light-scattering film can also be obtained by (4) the methodwhich comprises mixing the materials (melt-kneading components) togetherin solution and forming the anisotropic scattering sheet by use of themixture by, for example, a casting method.

The melting temperature is not lower than the melting points of theresins (continuous phase resin, dispersed phase resin), for exampleabout 150 to 290° C., and preferably about 200 to 260° C. The draw ratio(draft) may be for example about 2 to 40, preferably about 5 to 30, andmore preferably about 7 to 20. Incidentally, the draw ratio may forexample be about 5 to 80, preferably about 10 to 60, and more preferablyabout 20 to 40. The stretching factor (multiples) may for example beabout 1.1 to 50 (e.g. about 3 to 50), and preferably about 1.5 to 30(e.g. about 5 to 30).

When the drawing and stretching are conducted in combination, the drawratio may for example be about 2 to 10, preferably about 2 to 5, and thestretching factor may for example be about 1.1 to 20 (e.g. about 2 to20), and preferably about 1.5 to 10 (e.g. about 3 to 10).

In order to enhance the aspect ratio of the dispersed phase easily, thetechnologies include the method of subjecting the film (for example, afilm-formed (extruded or cast) and cooled film) to monoaxial stretching.The method for monoaxial stretching is not particularly restricted butincludes the method in which both ends of a solidified film are pulledin opposite directions (pull stretching), the method using two or morepairs of opposed rollers (2-roll sets) arranged serially (e.g. in aseries of 2 pairs) wherein the film is passed over the rollersconstituting each roll set by guiding it through the respective rollnips and stretched by driving the 2-roll set on the pay-out side at aspeed higher than the speed of the 2-roll set on the feed side(inter-roll stretching), and the method in which the film is passedthrough the nip of a pair of opposed rollers and stretched under theroll pressure (roll calendering).

The preferred monoaxial stretching technology includes methods whichfacilitate the mass production of film, such as inter-roll stretchingand roll-calendering. These methods are utilized as a first stretchingstep for producing a biaxial stretched film or a method for producing aphase film. Particularly, by roll calender method, not only anoncrystalline resin but also a crystalline resin can be easilystretched. Thus, when a resin sheet is stretched monoaxially, usuallythe trouble of “neck-in”, the phenomenon of local reduction in thethickness and width of the film, tends to occur. In the roll calendermethod, however, the trouble of “neck-in” can be precluded so that thefilm stretching operation is stabilized. Since there is no change(reduction) in film width before and after stretching and the filmthickness in the transverse direction can be made uniform so that thelight-scattering characteristic can be uniformized in the transversedirection of the film, the quality assurance of the product befacilitated, and the useful rate (yield) of the film be improved.Furthermore, the stretching factor can be freely selected from a broadrange. In addition, in roll calendering method, wherein the film widthcan be maintained before and after stretching, the reciprocal of therate of reduction in film thickness is approximately equal to thestretching factor.

The roll pressure for roll calendering may for example be about 1×10⁴ to1×10⁷ N/m (about 0.01 to 10 t/cm), and preferably about 1×10⁵ to 1×10⁷N/m (about 0.1 to 10 t/cm).

The stretching factor can be selected from a broad range and may forexample be about 1.1 to 10, preferably about 1.3 to 5, more preferablyabout 1.5 to 3. The roll calendering can be carried out at a thicknessreduction rate (draft) of about 0.9 to 0.1, preferably about 0.77 to0.2, more preferably about 0.67 to 0.33.

The stretching temperature is not particularly restricted inasmuch asthe film can be stretched and may be over the melting point or glasstransition point of the dispersoid resin (dispersed phase resin).Moreover, when a resin having a glass transition point or melting pointhigher than that of the dispersoid resin (for example, a resin having aTg or melting point higher by about 5 to 200° C., preferably about 5 to100° C.) is used as the continuous phase-forming resin and the film ismonoaxially stretched while the dispersoid resin is melted or softened,the aspect ratio of the dispersed phase particles can be increasedbecause the dispersoid resin is by far readily deformed as compared withthe continuous phase resin so that a film having a particularly largeanisotropy of light scattering can be obtained. The preferred stretchingtemperature may for example be about 100 to 200° C. (about 110 to 200°C.), and preferably about 110 to 180° C. (about 130 to 180° C.). Thecalender roll temperature, in case the continuous phase resin is acrystalline resin, maybe below the melting point of the resin or in theneighborhood of the melting point and, in case the continuous phaseresin is a noncrystalline resin, maybe a temperature below the glasstransition point and in the neighborhood of the glass transition point.

Incidentally, the above-mentioned laminated film can be obtained byusing a conventional method such as a co-extrusion and a lamination(e.g., a lamination by extruding, a lamination with adhesives) whichcomprises laminating the transparent resin layer on at least one side ofthe anisotropic scattering layer and orientating the dispersed phaseparticle by the orientation-treatment in the same manner as mentionedabove.

INDUSTRIAL APPLICABILITY

According to the present invention, use of a light-scattering sheethaving an anisotropic scattering characteristic enables to illuminate adisplay panel uniformly even when a plane or flat light source unit or adisplay apparatus (e.g., a liquid crystal display apparatus) comprises atubular light source having an anisotropic emission distribution(luminance distribution). That is, the sheet of the present inventionsuppresses the deterioration of the luminance depending on an anglerelative to a display surface of a display apparatus or device (inparticular, a transmittable display apparatus such as a transmittableliquid crystal display apparatus) and decreasing an angle dependence onthe luminance. Moreover, the sheet of the present invention enables tosimplify the structure of a plane or flat light source unit and adisplay apparatus or device (e.g., a liquid crystal display apparatus),and illuminates a display panel uniformly to realize clear visualrecognition of a display data. Furthermore, the sheet of the presentinvention ensures expansion or enlargement of a visual angle relative toa display surface and visual recognition the display surface with highluminance.

Furthermore, a combination of an anisotropic scattering sheet with aprism sheet insures inhibition of the deterioration of the luminancedepending on an angle relative to a display surface of a displayapparatus (e.g., a transmittable display apparatus such as atransmittable liquid crystal display apparatus) and improvements inviewing angle properties. Moreover, the sheet of the present inventionenables to expand or enlarge the viewing angle (particular, a viewingangle in a certain direction) relative to a display surface and torecognize the display surface visually with high luminance. Furthermore,the sheet of the present invention is capable of suppressing thedeterioration of the luminance in the certain direction even when anangle of a display surface exceeds 20°. Thus, the transmittable liquidcrystal display apparatus can be utilized without effecting eyestrain.

EXAMPLES

The following examples illustrate the present invention in furtherdetail without defining the scope of the invention.

The characteristics of the anisotropic scattering sheet, the plane orflat light source unit comprising (or using) the sheet and thetransmittable liquid crystal display apparatus comprising (or using) thesheet in the examples and comparative example were evaluated by thefollowing methods.

[Anisotropy]

Using the measuring system illustrated in FIG. 5, the intensity F ofscattered light at the scattering angle θ was measured. The orientatingor stretching direction of the anisotropic scattering sheet wasdesignated as X-axial direction and the direction perpendicular to thisdirection was designated as Y-axial direction.

[Luminance of Plane or Flat Light Source Unit]

For a backlight unit removed from a transmittable liquid crystal displayapparatus and for a backlight unit comprising an anisotropic scatteringsheet instead of a protective sheet of the removed backlight unit, theangle dependence on the luminance in the lateral direction (horizontaldirection) was measured by disposing a luminance meter 91 (manufacturedby MINOLTA Co., Ltd, LS-110) on the front of a backlight unit 92(manufactured by Mitsubishi Electric Co., Diamond Crysta RD152A), asshown in FIG. 6. The angle dependence was measured by rotating thebacklight unit 92 at a given angle.

[Luminance of Transmittable Liquid Crystal Display Apparatus]

For a transmittable liquid crystal display apparatus without theanisotropic scattering sheet, and for a transmittable liquid crystaldisplay apparatus comprising the anisotropic scattering sheet as shownFIG. 4, the angle dependence on the luminance in the lateral direction(horizontal direction) was measured by disposing a luminance system asshown FIG. 6 on the front of the transmittable liquid crystal displayapparatus.

Example 1

As the continuous phase resin, 60 parts by weight of crystallinepolypropylene-series resin PP (manufactured by Grand Polymer Co.;F109BA, refractive index 1.503); as the dispersed phase resin, 36 partsby weight of noncrystalline copolyester-series resin (PET-G,manufactured by Eastman Chemical Company; Eastar PETG GN071, refractiveindex 1.567); and as the compatibilizing agent, 4 parts by weight ofepoxidized diene-series block copolymer resin (manufactured by DaicelChemical Industries, Ltd.; Epofriend AT202; styrene/butadiene 70/30 (byweight), epoxy equivalent 750, refractive index about 1.57) were used.The refractive index differential between the continuous phase resin andthe dispersed phase resin was 0.064.

The above continuous phase resin and dispersed phase resin were dried at70° C. for about 4 hours, and kneaded these resins in a Banbury mixer.Using an extruder of multi-layered type, the kneaded product for forminga center or intermediate layer and the continuous phase resin(polypropylene-series resin) for forming a surface layer wererespectively melted at about 240° C. and extruded from a T-die with adraw ratio of about 3 onto a cooling or chilling drum of a surfacetemperature of 25° C. to laminate 25 μm of the surface layer (atransparent resin layer) on both sides of 200 μm of the center layer forobtaining a laminated sheet having three-layered structure (250μm-thick). Observation of the center layer by transmission electronmicroscopy (TEM) revealed that the dispersed phase in the center layerwas dispersed or distributed from in the form of approximate sphere-like(suborbicular) (the aspect ratio of about 1 and the average particulatesize of about 5 μm) to in the form of rugby ball-like configurationhaving a small aspect ratio (the aspect ratio of about 4, the dimensionof the major axis of about 12 μm, and the dimension of the minor axis ofabout 3 μm).

This sheet was monoaxially stretched by the roll calendering method(125° C., stretching factor of about 2 times (thickness reduction rateof about ½), width reduction rate of about 3%) to obtain a 125 μm-thickfilm. Observation of this film by TEM (dyeing with osmic acid) revealedthat the dispersed phase of the canter layer was shaped like a highlyelongated fiber, with a mean major axis dimension of about 30 μm and amean minor axis dimension of about 1.5 μm.

By measurement of the light-scattering characteristic of thus obtainedanisotropic scattering sheet, remarkable light-scattering anisotropy wasobtained as shown in FIG. 7. Moreover, in the light-scatteringcharacteristic, Fy(4°)/Fx(4°) was 8.2. With respect to the scattering inthe Y-axial direction showing intense scatter, Fy(0°)/Fy(30°) was 20.6and the scatter was observed in the wide angle.

A liquid crystal cell unit was removed from a commercially available 15inches-transmittable liquid crystal display apparatus to disassemble.The display apparatus was composed of a diffusing sheet, a prism sheetand a protective sheet which were disposed on a light guide of abacklight unit initially. As shown in FIG. 4, the anisotropic scatteringsheet was disposed instead of the protective sheet in such a directionas the main scattering direction of the anisotropic scattering sheet(X-direction) is directed to the lateral direction (horizontaldirection) to obtain a backlight (plane or flat light source unit)without a liquid crystal cell. The angle dependence on the luminance(but in the horizontal direction) was measured for the backlight by themethod as shown in FIG. 6. Incidentally, concerning the uniformity ofthe luminance, N(0°)/N(18°) and N(18°)/N(40°) were calculated as theluminance of the front side (N(0°)) was 1.

Comparative Example 1

A liquid crystal cell unit was removed from the commercially available15 inches-transmittable liquid crystal display apparatus to disassemble.The angle distribution on the luminance was measured by using theremoved backlight unit singly in the same manner as Example 1. Thelight-scattering characteristic of the protective sheet disposed on thebacklight unit was measured by the method as shown in FIG. 5 in the samemanner as Example 1. As a result, no anisotropy of the scattering wasobserved and Fy(4°)/Fx(4°) was 1.0. Regarding the scattering in thelateral direction (horizontal direction), the scattering intensity inthe wide angle was small, and Fy(0°)/Fy(30°) showed a large value(1,000).

Example 2

The above continuous phase resin and dispersed phase resin weremelt-molded in the same manner as Example 1, and extruded from a T-dieat a draw ratio of about 6 onto a cooling drum having a surfacetemperature of 25° C. The total thickness of the obtained sheet was 125μm, and an anisotropic scattering sheet was composed of alight-scattering layer as the center layer having a thickness of about100 μm and surface layers formed by a continuous phase resin on bothsides the scattering layer and each having about 12.5 μm thickness.

Observation of the micro-structure of thus obtained sheet in the samemanner as Example 1 revealed that the dispersed phase of the centerlayer showed like an elongated fiber, with a mean major axis dimensionof about 15 μm and a mean minor axis dimension of about 2 μm.Measurement of the light-scattering characteristic of thus obtainedanisotropic scattering sheet revealed that Fy(4°)/Fx(4°) was 2.4, withrespect to the scattering in Y-axial direction showing considerablescattering, Fy(0°)/Fy(30°) was 8.4 which presents the wide anglescattering, though the light-scattering characteristic was smallercompared with Example 1.

Example 3

An original sheet having a three-layered structure for roll-calenderingwas produced in the same manner as in Example 1. The sheet wasmonoaxially stretched by the roll calendering method (125° C.,stretching factor of about 2.5 times (thickness reduction rate of about0.4), width reduction rate of about 3%) to obtain a 100 μm-thick film.Observation of the micro-structure of the sheet in the same manner as inExample 1 revealed that the dispersed phase of the center layer had ahighly elongated fiber, with a mean major axis dimension of about 40 μmand a mean minor axis dimension of about 1.3 μm.

Example 4

As the continuous phase resin, 80 parts by weight of a crystallinepolypropylene-series resin PP (manufactured by Grand Polymer Co.; F133,refractive index 1.503); as the dispersed phase resin, 18 parts byweight of a polystyrenic resin GPPS (general-purpose polystyrenic resin,manufactured by Daicel Chemical Industries, Ltd., GPPS #30, refractiveindex 1.589); and as the compatibilizing agent, 2 parts by weight of anepoxidized diene-series block copolymer resin (manufactured by DaicelChemical Industries, Ltd.; Epofriend AT202; styrene/butadiene=70/30 (byweight), epoxy equivalent 750, refractive index about 1.57) were used.The refractive index differential between the continuous phase resin andthe dispersed phase resin was 0.086.

A sheet having a three-layered structure was produced in the same manneras in Example 1. Observation of the micro-structure of the sheet in thesame manner as in Example 1 showed that the dispersed phase of thecenter layer had an elongated fiber configuration, with a mean majoraxis dimension of about 20 μm and a mean minor axis dimension of about1.6 μm.

Example 5

The anisotropic scattering sheet obtained by Example 1 was disposed onthe backlight in the same manner as in Example 1, and the liquid crystalcell was rebuilt into the apparatus to obtain a transmittable liquidcrystal display apparatus. The device was driven or operated, and theangle dependence on the luminance was measured in the same manner as inExample 1 with white color display.

Comparative Example 2

A commercially available transmittable liquid crystal unit was turnedinto white color display without altering the display condition, and theangle dependence on the luminance was measured in the same manner as inExample 1.

The anisotropic scattering characteristics of the films obtained byExamples and Comparative Examples, as well as the angle dependence onthe luminance for the backlight and at the display condition of theliquid crystal display apparatus were evaluated. The results are shownin Table 1.

Moreover, FIG. 7 shows the anisotropic scattering characteristic of thefilm obtained by Example 1. Incidentally, visibility from the inclineddirection was evaluated according to the following criteria.

-   A: the display can be visually recognized clearly (or finely) when    the display is looked in or at the inclined horizontal direction    relative to the front surface-   B: the display is recognized visually when the display is looked in    or at the inclined horizontal direction relative to the front    surface-   C: it is difficult to recognize the display visually when the    display is looked in or at the inclined horizontal direction    relative to the front surface

TABLE 1 Visibility Scattering from the Luminance Luminance ratiocharacteristic inclined N(θ) N(θ)/N(θ) Fy(4)/Fx(4) Fy(0)/Fy(30)direction θ = 0° θ = 18° θ = 40° N(0)/N(18) N(18)/N(40) Ex. 1 8.2 20.6 A1.20 1.21 1.29 0.99 0.94 Com. Ex. 1 1 1000 C 1 0.91 0.71 1.10 1.28 Ex. 22.4 8.4 A 1.31 1.36 1.36 0.96 1.00 Ex. 3 81 111 B 1.25 1.28 1.21 0.981.05 Ex. 4 3.0 11.2 B 1.58 1.61 1.68 0.98 0.96 Ex. 5 8.2 20.6 A 0.540.55 0.58 0.99 0.94 Com. Ex. 2 1 1000 C 0.45 0.41 0.32 1.09 1.28

It is apparent from Table that the sheets according to Examples havehigh anisotropy as compared with the sheets prepared by ComparativeExamples. Thus, in case of employing the sheets according to Examplesfor a backlight unit, the angle dependence can be reduced, and thedeterioration of the luminance is inhibited even when the display islooked in the inclined direction.

Regarding the evaluation for the liquid crystal display apparatus, asshown in Example 5 of Table 1, since the liquid crystal cell adsorbsabout half amount of alight, the total luminance was deteriorated.However, the uniformity of the luminance was equal to Example 1.Moreover, even when the display was looked in the inclined direction,the prominent change in brightness was not observed as same asExample 1. On the other hand, as apparent from Comparative Example 2 ofTable 1, the conventional liquid crystal display apparatus deterioratedthe luminance wholly and, as in the case with Comparative Example 1,showed a larger value of the luminance ratio than Example 1, and whenthe display was looked in the inclined direction, the prominent changesin brightness observed with decreasing the prominent deterioration inthe luminance as the inclined angle was larger.

1. An anisotropic scattering sheet adapted to scatter an incident lightin a light-advancing direction and having a light-scatteringcharacteristic F(θ) satisfying the following expression representing arelation between a light-scattering angle θ and a scattered lightintensity F over a range of θ=4 to 30°:Fy(θ)/Fx(θ)>2 wherein Fx(θ) represents the light-scatteringcharacteristic in a direction of an X-axis and Fy(θ) represents alight-scattering characteristic in a Y-axial direction which isperpendicular to the X-axial direction; wherein the light-scatteringcharacteristic Fy(θ) is decreased gradually with increasing thelight-scattering angle θ and wherein the light-scattering characteristicsatisfies the following expression representing the relation between thelight-scattering angle θ and the scattered light intensity F over arange of θ=0 to 30°: 10<Fy(0°)/Fy(30°)<150; and wherein the sheet iscomposed of a continuous phase comprising a crystalline resin and adispersed phase particle comprising a noncrystalline resin. which phasesare different in refraction index by not less than 0.001 from eachother, wherein the mean aspect ratio of the dispersed phase particles islarger than 1 and the major axes of the dispersed phase particles areoriented in the X-axial direction of the film.
 2. An anisotropicscattering sheet according to claim 1, wherein the scatteringcharacteristic Fx(θ) and the scattering characteristic Fy(θ) satisfy thefollowing expression over a range of θ=4 to 30°:Fy(θ)/Fx(θ)>5.
 3. An anisotropic scattering sheet according to claim 1,adapted to scatter the incident light in the light-advancing directionand having the light-scattering characteristic F(θ) satisfying thefollowing expression representing the relation between thelight-scattering angle θ and the scattered light intensity F over arange of θ=2 to 30°:Fy(θ)/Fx(θ)>5.
 4. An anisotropic scattering sheet according to claim 3,wherein the scattering characteristic Fx(θ) and the scatteringcharacteristic Fy(θ) satisfy the following expression over a range ofθ=2 to 30°:Fy(θ)/Fx(θ)>10.
 5. An anisotropic scattering sheet according to claim 1,wherein the scattering characteristic satisfies the following expressionover a range of θ=0 to 30°:15<Fy(0°)/Fy(30°)<50.
 6. An anisotropic scattering sheet according toclaim 1, wherein the mean aspect ratio of the dispersed phase particlesis 5 to
 1000. 7. An anisotropic scattering sheet according to claim 1,wherein the mean dimension of the minor axes of the dispersed phaseparticles is 0.1 to 10 μm.
 8. An anisotropic scattering sheet accordingto claim 1, wherein the thickness of the sheet is 3 to 300 μm and thetotal light transmittance of the sheet is not less than 85%.
 9. Ananisotropic scattering sheet according to claim 1, wherein the ratio ofthe continuous phase relative to the dispersed phase is (the continuousphase/the dispersed phase)=99/1 to 50/50 (weight ratio).
 10. Ananisotropic scattering sheet according to claim 1, wherein thecontinuous phase comprises a crystalline polypropylene-series resin. 11.An anisotropic scattering sheet according to claim 1, wherein thedispersed phase comprises at least one member selected from anoncrystalline copolyester-series resin and a polystyrenic resin.
 12. Ananisotropic scattering sheet according to claim 1, wherein the sheetfurther comprises a compatibilizing agent for the continuous phase andthe dispersed phase.
 13. An anisotropic scattering sheet according toclaim 12, wherein the compatibilizing agent comprises an epoxidizeddiene-series block copolymer.
 14. An anisotropic scattering sheetaccording to claim 1, wherein the sheet comprises a crystallinepolypropylene-series resin constituting a continuous phase, at least oneresin selected from a noncrystalline copolyester-series resin and apolystyrenic resin, which constitute a dispersed phase, and anepoxidized diene-series block copolymer constituting a compatibilizingagent, and wherein the ratio of the continuous phase relative to thedispersed phase is (former/latter)=99/ 1 to 50/50 (weight ratio), andthe ratio of the dispersed phase relative to the compatibilizing agentis (former/latter)=99/1 to 50/50 (weight ratio).
 15. An anisotropicscattering sheet according to claim 1, wherein the sheet is formed withsurface irregularities extending in the direction of the X-axis of thefilm or the major axis of the dispersed phase.
 16. A display apparatus,which comprises a display unit, and a plane light source unit recited inclaim 1 for illuminating the display unit.
 17. A display apparatusaccording to claim 16, wherein the display unit comprises a transmissiontype unit.
 18. A display apparatus according to claim 16, wherein thedisplay unit is a liquid crystal display unit.
 19. A display apparatusaccording to claim 16, an anisotropic scattering sheet is disposed insuch a direction that a main light-scattering direction of the sheet isaddressed or directed to the horizontal direction of the display surfaceof the display unit.
 20. A plane light source unit, comprising: atubular light source; a light guide member for being incident a lightemitted by the tubular light source from the lateral side of the lightguide member and emerging the light from an emerge surface; and at leastone anisotropic scattering sheet interposed between the light guidemember and a display unit for illuminating the display unit uniformly bythe light from tubular light source, wherein said anisotropic scatteringsheet comprises an anisotropic scattering sheet having alight-scattering characteristic recited in claim
 1. 21. A plane lightsource unit according to claim 20, wherein the unit comprises aplurality of anisotropic scattering sheets composed of a continuousphase and a dispersed phase which are different in refraction index fromeach other, the dispersed phase is dispersed in the continuous phase andthe mean aspect ratio of the dispersed phase is larger than 1, andwherein the plurality of anisotropic scattering sheets are disposedbetween the light guide member and the display unit with orientingdifferent light-scattering directionality from each other.
 22. A planelight source unit according to claim 21, wherein two anisotropicscattering sheets are disposed between the light guide member and thedisplay unit with addressing or directing the major axes of thedispersed phase to a perpendicular direction each other.
 23. A planelight source unit according to claim 20, wherein the anisotropicscattering sheet comprises a continuous phase and a dispersed phasewhich differ in refraction index by not less than 0.001, the mean aspectratio of the dispersed phase is larger than 1 and the major axis of thedispersed phase is oriented in th axial-direction of the tubular lightsource.
 24. A plane light source unit according to claim 20, whereinassuming that the axis-direction of the tubular light source is X-axialdirection, the anisotropic scattering sheet is disposed in such mannerthat a main light-scattering direction along th Y-axial direction isperpendicular to the axial-direction of the tubular light source.
 25. Aplane light source unit according to claim 20, which comprises anisotropic diffusing sheet interposed between the light guide member andthe display unit, a prism sheet, and an anisotropic scattering sheethaving a light-scattering characteristic recited in claim
 1. 26. A planelight source unit according to claim 25, wherein the anisotropicscattering sheet is positioned at the front side of the prism sheet. 27.A plane light source unit according to claim 20, wherein the tubularlight source is disposed in almost parallel with and adjacent to thelateral side of the light guide member, a refractive member is disposedat or on the back side of the light guide member for reflecting a lightfrom the tubular light source to the display unit side, and theanisotropic scattering sheet is interposed between the light guidemember and the display unit.